1. Field of the Invention:
This invention relates to a driving device for the optical scanning unit of electrophotographic reproducing apparatus.
2. Description of the Prior Art:
The electrophotographic reproducing apparatus has two types of exposing a material to be copied: in one type the copy board is moved and in other type the optical scanning unit is moved. The optical scanning unit consists of a document illuminating lamp, a group of mirrors and a focusing lens, all arranged under the copy board installed on the upper portion of the reproducing apparatus. Either the copy board of the optical scanning unit is made to reciprocate in synchronism with the copying operation. In the electrophotographic reproducing apparatus whose magnifying ratio can be changed the scanning speed of the optical scanning unit is varied in accordance with the magnifying ratio. In the conventional copying machine, the driving speed of the scanning unit is changed by changing the engagement of gears from one gear to other gear with different number of teeth.
In such variable speed driving equipment which makes use of engagement of gears, the distance between the shafts of two gears in mesh is constant, so that it is difficult to obtain a desired combination of gears to change the speed ratio. To obtain the desired gear ratio, it is necessary to use a complicated speed change mchanism with more than two stages of gear trains or to change the distance between gear shafts. To change the distance between the gear shafts it is necessary to replace the frame supporting the gear shafts and this will make the mechanism complex. When it is desired to change the speed ratio, with the driving mechanism assembled into the electrophotographic reproducing apparatus, it is necessary to remove the frame to replace the gears.
Thus, the conventional practice is to prepare the optical scanning unit driving device for each different speed ratio and, when changing the speed ratio, replace the whole device. This method is relatively simple in replacement work since the whole unit is replaced, but has disadvantages that since each unit contains frame, shaft and clutches the unit is heavy and expensive.